In most towns and cities today there can be many types of air pollution. This pollution can include, and is not limited to, smog, acid rain, CFC's and others. Smog is a type of large scale outdoor pollution that is usually caused by chemical reactions between pollutants derived from different sources including automobile exhaust and industrial emissions. Cities are often the locale for this type of pollution and many cities suffer from the effects of smog, particularly during the warm months of the year. Smog can include fine particles which are emitted directly as smoke and diesel soot. Other components of smog can include nitrogen oxide which is produced as fossil fuels are burned as well as carbon monoxide. The cause of smog varies depending on the city. The geographical location, temperature, wind and weather factors can affect the smog. A temperature inversion can exacerbate smog because pollution can not rise and be dispersed. Cities surrounded by mountains also experience trapping of pollutants and as a result, problems with smog. Smog can cause aching lungs, coughing, headaches and other ailments. Ozone is frequently a component of smog. Studies on animals show that ozone damages the cells in the lung airways causing inflammation and swelling. Ozone also reduces the respiratory system's ability to fight infection and remove foreign particles. Ozone may also provide a particular health threat to the young, the old and those who suffer from cardiovascular problems. Studies performed by the University of Southern California have concluded that smog is particularly damaging to children. These studies have concluded that smog can have subtle, long term effects on children's lungs and may cut girls breathing capacity more than boys. The impaired breathing capacity, i.e. a reduced volume or flow of air in the lungs, can leave children vulnerable to respiratory diseases and underdeveloped lungs. Boys who are subjected to smog are particularly susceptible to respiratory illnesses. The studies have also shown that smog can cause asthma. As a result, when smog is present, outdoor activities should be curtailed to avoid exposure to the smog. Another type of air pollution is acid rain. When an acidic material such as sulfuric acid combines with water, the rain or snow becomes acidified. Acid rain can damage plants, the soil and change the chemistry of lakes and streams. Many parents of small children are troubled because of the air pollution problems. On the one hand, parents are desirous of letting children be outdoors. However, it is often difficult to gauge the amount of smog or other pollutants in a given area. As a result, many parents are unsure on any given day whether to permit their children to be outside and for how long. The problem is particularly acute where infants and small children are concerned. As a result, many parents seek to avoid the risk of air pollution. Most infants and small children are particularly susceptible to the deleterious effects of air pollution. Many parents are reluctant to bring their small children outside on days when there is any question about the quality of the air. Parents who have children in strollers or baby carriages frequently use clear plastic covers over the stroller or carriage to keep the pollutants out. While the cover can assist the child, it does not solve the problem completely. First, the plastic cover should not create an airtight seal as it could suffocate the child. As a result, the plastic cover should be relatively porous to outside air as the child needs to breathe and eliminate the risk of suffocation. Unfortunately, the porosity of the cover permits the child to breathe the air that the child should frequently be protected from. The plastic cover also does nothing to improve the quality of the air breathed by the child.